1. Field of the Invention
The invention relates to a chip package, and, more specifically, to a chip package with a specific pad between a bonding wire and an aluminum pad exposed by an opening in a passivation layer or between a bonding wire and an aluminum cap, leading the intermetallic compound (IMC) to be avoided.
2. Brief Description of the Related Art
Wirebonding is the process of providing electrical connection between a semiconductor chip and an external circuit using very fine bonding wires. The wire used in wirebonding is usually made either of gold (Au).
Referring to FIG. 1, in the prior art of a BGA (ball grid array) package, one end of a gold wire 110 is ball bonded to an aluminum cap 114 over a copper pad 120 exposed by an opening 118a in a passivation layer 118 of a semiconductor chip 112, and the other end of the gold wire 110 is wedge bonded to a BGA substrate 116. The copper pad 120 of the semiconductor chip 112 can be electrically connected to a solder ball 122 under the BGA substrate 116 via the gold wire 110 and a metal trace of the BGA substrate 116.
However, the intermetallic compound (IMC) could be formed the gold wire 110 and the aluminum cap 114 in the following high-temperature packaging process, such as in the lead-free ball planting process. The intermetallic compound has a brittle structure, leading a poor reliability for the BGA package. Besides, the gold wire 110 in a high-power application could be heated at a high temperature, which also could lead the undesired intermetallic compound (IMC) formed the gold wire 110 and the aluminum cap 114.